We have used high-temperature ab initio Density Functional (DF) simulations to study the Equation of State (EoS) of orthorhombic MgSiO3 perovskite under lower mantle pressure-temperature conditions. We have determined the Gruneisen parameter (y) as a function of volume. The product of the volume coefficient of thermal expansion and the bulk modulus is nearly constant at temperatures higher than the Debye temperature. Using this relation allows predicting the values of the bulk modulus. The variation in isothermal bulk modulus with an increase in temperature is found to be related linearly with the change in the temperature. The good correlations to the experiments indicate that the expression may be useful for substances for which elastic data are lacking.Our state-of-the-art simulations, accurate to within 10%, resolve the long-standing controversy on thermal expansion (a) and Gruneisen parameter (y) of MgSiO3 perovskite. Under ambient conditions we find the values for a and y to be 1.86 x10 -5K 1 and 1.51 respectively, in excellent agreement with the latest experimental studies.
Keywords: Perovskite, Equations of state, Density Functional Theory.